running on unleaded !!

[Bryanj]

Silver top black second and there will be a small mark close to the gap and it goes at the top

[Johnwebley]

John,

I recently had some rings for the 550 from silvers.
The rings are slightly different if you look at them one is square and the other slightly tapered.
It tells you the installation sequence in the manual if you have one, the rings are marked with a "N" this needs to go to the top if I remember correctly.
Hope this helps.

Regards,

thanks,I looked Very Hard,and found the "N"s,as luck would have it,I had fitted them correctly,
as far as the cause,
check out this link,
http://www.motorcycleclassics.com/mc-how-to/project-cafe-rebuilding-a-1973-honda-cb500.aspx#axzz2Vx8B1Md3


a CB500/4 with almost the same issue,
my piston wasn't quite as bad,but the diagnosis is "detonation" ,I guess severe "pinking" ??
my bike never seemed to suffer this,but would over advanced ignition cause it ?
I run Boyer electronic and also a much bigger plug gap,(0.033th) as it supports a bigger spark,
also gives great low/mid range punch,
maybe I should retard the ignition a few degrees ??

thoughts and comments please,

John

[Johnwebley]

update,

all back together,

started first time.

 felt really tight,the new rings are steel,see link,look for motorcycle rings
http://www.npr.co.jp/english/products/p_train/index.html

I expect these to be stronger,less brittle,and more durable than old style cast rings

after about 130 miles,gentle throttle no more than 5k under load,and 6k on overrun

the motor feels much better,still a little tight,but very torquey

will continue till about 500 miles before any serious throttle,increasing the revs under light load

[Johnwebley]

update,

 firstly thank you all for your help and advise,

the bike is back together,just over 600 miles,runs beautifully,got its top end back,

runs up to 9k very willingly,

oil change done,no issues,seems so much more in the lower gears,

I rev it in the 2nd,3rd , and 4th gears,dont slog it in top,

and I am really pleased

John

[Bryanj]

Thats not detanation as the cause, what happens is some idiot PO reved the nuts off it when cold and the rings expand to quickly so the top one shatters into pieces, this widens the ring groove then flame passage and heat finish it off.

Used to happen quite a bit on 250K4 and CB175's

[florence]

I had exactly this on a 550 years ago.  My friend bought a bike that had been standing for a year or so.  Unfortunatley, the seller had taken the bike for a blast to make sure all working OK.  My friend bought the bike but soon complained that it wasn't running properly and was smoking.  When I investigated I discovered that there were broken rings on all four cylinders.  Luckily, they had stayed in place and not scored the bore and a new set was all that was needed.

[Johnwebley]

Thats not detanation as the cause, what happens is some idiot PO reved the nuts off it when cold and the rings expand to quickly so the top one shatters into pieces, this widens the ring groove then flame passage and heat finish it off.

Used to happen quite a bit on 250K4 and CB175's

I had exactly this on a 550 years ago.  My friend bought a bike that had been standing for a year or so.  Unfortunatley, the seller had taken the bike for a blast to make sure all working OK.  My friend bought the bike but soon complained that it wasn't running properly and was smoking.  When I investigated I discovered that there were broken rings on all four cylinders.  Luckily, they had stayed in place and not scored the bore and a new set was all that was needed.

 thanks for the hints !!

I can't remember racing it when cold,

BUT,from now on will keep it below about 5k for a couple of miles at least,

thanks

John